The concept of “universal basic income” is gaining currency right now in Silicon Valley, where thinkers from Tesla’s Elon Musk to Facebook’s Mark Zuckerberg are considering the idea of blunting the impact of automation by driving each person—working or not—with a minimum income for life. As Fortune reports this month, venture investor Sam Altman and his startup incubator firm, Y Combinator, are currently testing the idea with a pilot project involving up to 100 families in Oakland, Calif.

But the idea is hardly new: In fact, it has resurfaced repeatedly over the centuries at times of economic transformation, winning allies across the ideological spectrum. Here are some of the thinkers and policymakers who have backed it over the years.

Thomas More

The English lawyer and statesman served as a counselor to Henry VIII at a time of tremendous social, religious and economic upheaval. In his novel Utopia (1516), More advocated using basic income to share the wealth that was generated as public lands passed to private ownership. The novel, originally written in Latin, helped spawn a centuries-old genre of literature about “utopian” (ideal) societies.

Thomas Paine

In the 1790s pamphlet Agrarian Justice, the American Founding Father called for a “citizen’s dividend”—a payment made to all U.S. citizens, paid for by a tax on landowners. Many of Paine’s ideas were considered radical for their time; indeed, when he wrote the pamphlet, he was advising leaders in revolutionary France. But many historians now see Agrarian Justice as one of the intellectual foundations of the Social Security entitlement program.

Milton Friedman

Economics Friedman 1976 — Eddie Adams — AP

The champion of free markets became famous in the 1980s as a prominent adviser to President Ronald Reagan and U.K. Prime Minister Margaret Thatcher. But as far back as 1962, Friedman had endorsed basic income, arguing that it would be more efficient than the welfare bureaucracy at alleviating the problems of low-income households. Other thinkers associated with the so-called Chicago school of conservative-leaning economics, including Friedrich Hayek, also endorsed the idea, though it has seldom been embraced by the elected officials they’ve advised.

Dr. Martin Luther King Jr.

Over his years as a civil-rights activist, King came to see economic equality and racial equality as fundamentally intertwined, and he began urging the federal government to do far more to lift people out of poverty. In his final book, Where Do We Go From Here? (1967), King called for a basic income “pegged to the median of society.”

Richard Nixon

The Republican President’s administration ran UBI experiments in several states from 1968 to 1971, finding, among other things, that it had no negative effect on work ethic. Two of the people Nixon tasked with conducting the experiments rose to prominent roles in the administration of George W. Bush: Donald Rumsfeld, director of the Office of Economic Opportunity, who became defense secretary under Bush; and Rumsfeld’s special assistant, Dick Cheney, who served as Bush’s Vice President.

Pierre Trudeau

The Canadian leader’s mid-1970s “Mincome” project remains among the largest UBI programs ever pursued in an advanced economy, reaching several thousand households, primarily in the province of Manitoba. Trudeau’s son, Justin, is now Canada’s prime minister, and the UBI idea lives on in the country, with a trial program due to launch in Ontario this summer.

A version of this article appears in the July 1, 2017 issue of Fortune as part of the feature titled “Why Free Money Could Be the Future of Work.”